Method and apparatus for support and cooling of shell molds



May 30, 1961 R. T. CARTER METHOD AND APPARATUS FOR SUPPORT AND COOLINGOF SHELL MOLDS 2 Sheets-Sheet 1 Filed Dec. 18, 1959 R. T. CARTER May 30,1961 METHOD AND APPARATUS FOR SUPPORT AND COOLING OF SHELL MOLDS 2Sheets-Sheet 2 Filed Dec. 18, 1959 METHOD AND APPARATUS F OR SUPPORT ANDCOOLING F SHELL MOLDS This invention relates to casting procedures, andmore particularly it is concerned with a method and apparatus for thesupporting and cooling of a shell mold during and/ or after filling theshell mold with molten metal.

Progress in the sand foundry and the investment foundry has recentlybrought about the use of comparatively thin refractory shell molds inwhich material is usually built up in layers to provide a thin Walled,low mass, highly gas permeable ceramic shell. Such a shell mold is fullydescribed, for example, in Patent Nos. 2,806,269 or 2,806,- 270, issuedSeptember 17, 1957. This ceramic shell mold has superior fillingcharacteristics as well as enabling more rapid cooling due to thedecreased mass of insulating refractory material. The advent of this newconcept in metal casting, however, has brought with it new problems,many of which have not been encountered before. Among these are theproblems relating to the provision of means for adequately supportingthe thin walled mold during and after pouring, and the provision ofmeans for suitably controlling the cooling rate of the casting. In thisnew field the accent ison the speed of fabrication and on casting atminimum costs. The foundryman therefore wishes to have a mold which isconstructed with a minimum amount of material and which can becastWithout the need of costly backups and supporting structure andprocedures and yet incorporates all the advantages which accrue throughthe use of thin walled refractory types of molds.

it is therefore a primary object of this invention to provide a methodand apparatus by which thin walled shell molds may be cast which provideoutward support of theshell without resorting to the costly conventionalbackup and supporting procedures.

It isa further important object of this. invention to provide a methodand apparatus for increasing the rate of-cooling of shell type molds ina manner which is simple and economical.

XStill another object of the invention is to provide a simple andexpeditious method of supporting an irregularly shaped mold in thepouring operation.

Another important object of this invention is to provide a method andapparatus by which a variable rate of coolin'gon different parts of theshell mold can be achieved. in. accordance with principles of theinvention there is provided a structure having upper and lower chamberswhich are divided by a porous membrane. The upper chamber is open to theatmosphere and is filled with a bed of fine grain heat-conductivematerial such as metal grit, zircon, silica sand, etc. The shell moldtobe poured is placed on top of this prepared bed, and during or afterpouring, gas underpressure, introduced intothe lower chamber, permeatesthrough the membrane in such a manner as to cause the particles ofconductive material in the} upper. chamber to be displaced from eachother, substantially in floating condition. The shell mold thus becomessubstantially unsupported and lowers itself gradually into the floatingparticles. When the pressure is removed'the particlesret'urn by gravityto 'a stable conditates Paent tion completely surrounding and supportingthe shell inv the form of a gas permeable heat sink. Support and a'controlled cooling environment for the shell are thus' simultaneouslyprovided. After suificient cooling time has been allowed the pressure isagain applied through the membrane and causes flotation of, the coolingparticles.'

The shell and casting then may be easily removedfrom. the bed. Uponsubsequent release of pressure the. bed' is again ready to receiveanother shell. The invention thus provides a steady support of thinwalled shell molds during the cooling period and through judiciousselection,

cooling particles the cooling rate of the casting can be} controlled.

Additional objects and advantages of the invention will} Fig. 3 is asectional view of another container of the v apparatus taken along theline 3-3 of Fig. l;

Fig. 4 is a view of a plurality of the containers utilized in theapparatus, the view being taken along the line 4-4 of Fig. l; and

Fig. 5 is a sectional view of a container illustrating a modified formof cooling bed by means of which selected areas of the casting may becooled at different rates.

The apparatus shown in Figs. 1-4 enables the provi sion of controlledsupport and cooling of shell moldsin a substantially continuous castingoperation. As shown in Fig. l twelve steel tank structures are mountedon a turntable bed plate 12. Each tank structure is divided into-anupper compartment, 14 and a lower compartment. 16 by a permeablemembrane 18 as shownin Fig. 2. A valve 20, associated with an air supplypipe 22, controls introduction of air pressure to the lower charnberiofeach tank. The valve 20 is operated by means of an actuating lever 24pivotally mounted on the tank walland a connecting link 26. A dump valve28, positioned on the opposite side ofeach lower chamber from valve; 20,is adapted to be operated by a cam 30, two of which are secured to thefloor 32 at spaced points adjacent the" turntable 12.

Positioned in the upper chamber is a bed 34 of a finej grainedheat-conductive material. Depending on the do-1 sired characteristicsthis may be an iron grit, azircon, sand or other similar material indiscrete particle form.

The turntable 12 is bolted to a central member36 which is mounted forrotation on a suitable pedestal sup-r port 38 which is mounted on thefloor 32 as shown in; Fig. 3. A set of bearings 40, positioned betweenthe sup:

port 38 and central turntable member 36 permit rotation" of theturntable as driven by suitable means (not shown): Air or anothersuitable fluid medium is supplied under pressure through conduit 44 tothe interior of the pedestal support and through a horizontal passageway46 to a can? nelure-48. An aperture 50 on thero'tating central mern; ber36 communicates with distributing pipe 52 whic is; in turn connected. tothe circular conduit '22. A valve, operating mechanism 54 is alsosecured to the; pedestal support 38 and includes two cam units 56, 58which operate the valve levers 24. When a cam engages a leverit:operates the associated valve 20 through linkage 26 so that air pressureis supplied to the lower chamber 16 and through the membrane 1 8 so thatthe particles of the bed 34 in the upper chamber 14 rise and becomeslightly sepa; rated from each other. The volume occupied by'lthdparticles increases slightly and theytend to beha a manner similar'tothat efafiuid;

Patented May 30, 1961 The operating stations adjacent the turntable 12include a mold loading station at which there is provided a conveyer 60for shell molds 62, a pouring station at which there is a pouring ladle64 and a removing station at which there is provided a conveyer 66 forremoving the cast and cooled shell molds.

In operation a shell mold 62 which has been preheated to temperaturesranging from about 400 to 1800 F. is placed on top of theheat-conductive bed 34 from the conveyer 60 shown in Fig. 2. Theturntable carrying this shell is then moved to the pouring position andthe metal is poured into the mold from the ladle 64. On completing thispouring operation air is introduced into the lower compartment 16 as theassociated valve lever 24 of the tank contacts the cam 56. As the airpermeates through the membrance 18 the particles in the upper chamber 14become slightly separated and the cast shell sinks into the bed into aposition indicated generally in Fig. 3. When the cast shell reaches thedesired level in the bed 34 the air pressure is turned off as by releaseof the lever from the cam 56 and the dump valve is operated by cam 30 toremove any excess pressure in the lower chamber. The bed of materialparticles then has returned to a stable condition completely envelopingand supporting the cast shell. The turntable 12 continues to rotate andpasses through several positions which provides sufficient time for thecasting to cool the required degree and then the lever 24 is againoperated, this time by cam 58, to introduce pressure into the lowerchamber so that the bed of material is returned to a fluid condition andthe cast shell is removed from the bed and placed on the conveyer 66 forsuitable subsequent handling. The turntable 12 continues to rotate withair pressure remaining applied to the bed 34 so that the particles whichabsorbed heat from the cast mold in the cooling cycle are thenthemselves returned to suitable cool condition. The valve lever 24 ridesoff cam 58 just before the loading position, the air pressure valve isclosed and the bleed valve 28 is opened by the cam 30 for a short timeto remove any pressure in the lower chamber thus preparing the bed forthe loading of another shell.

Under some conditions it may be desirable that the cooling of the baseof the shell mold should be more rapid than the cooling of the remainderof the casting. This may be achieved by only partially immersing theshell in the heat conductive bed while it is in a fluid state andsecurely positioning the shell in that position for pouring by removingthe application of pressure. In this way the portion of the shellimmersed in the material bed will be at a lower temperature than theremainder of the shell and will impose a more rapid chill on thatportion of the casting. Further there are many instances in which it isnot convenient to construct a shell mold in such a manher that the shellwill stand stably on a level surface for pouring. Accordingly the methodand apparatus of the invention can be utilized so that shells of anyshape or configuration can be supported securely by the bed in thedesired pouring position without the necessity of other supportingmeans. Thus, air under pressure may be introduced into the bed to causethe particles to be displaced from each other before the pouringoperation to permit the lower portion of the shell to sink into the bed,after which the air under pressure to the bed is removed to permit theparticles to fall by gravity to rigidly support and position the shellin the bed. Thereafter, the molten material is poured into the shell,and air under pressure is again introduced to the bed to again displacethe particles and permit the filled shell to descend to a predetermineddepth in the bed. Thereafter, the air under pressure is again removed sothat the bed supports and cools the filled shell.

At the present time, there is considerable limitation with regard to thecross section of and the static head that can be retained by certainbonded type shell molds. By presently known techniques these problemscan be overcome to some extent by carefully packing the shell mold insand. However this procedure has disadvantages of time and cost and itis frequently difiicult to pack this type of mold so that the pressureis evenly distributed. The invention provides a ready solution to thisproblem by permitting the sinking of the shell into the supportingmedium prior to pouring. Side wall movement can be completely eliminatedand at the same time an excellent gas permeable heat sink is provided.The shell mold is removed in a similar manner as that described above.

Fig. 5 shows a significant modification of the invention. For the besteconomy in necessary feed metal it is often expedient to cool differentsections of the casting at different rates. Such results can be obtainedeconomically by the following procedure. The casting is oriented on thesprue in a manner so that the lower section thereof should preferablyfreeze first and so on progressively up to the top of the casting. Theparticles of the cooling bed comprise several different materials, eachhaving a different specific gravity and each possessing differentthermal transfer coefiicients. Materials of different specific gravitywill be suspended in the bed in layers by the pressure and will remainin the configuration on release of the pressure. As an example,referring to Fig. 5, there is provided in the upper chamber 14 of thecontainer 10 a layer 68 of mesh iron grit, a layer 70 of mesh zirconsand and a layer 72 of a suitable insulating material. The materialsremain in this general relationship throughout the entire operatingprocedure. Thus a shell may be cast at a given temperature and thenintroduced into supporting thermally conductive media which providevarying rates of heat transfer throughout the depth of the bed. In theillustrated case an insulating material has been used in the upper layerto prevent the sprue from freezing, thus improving the feed time forthis section.

A further example, indicative of still other advantages of theinvention, may be understood by considering the problems currentlyencountered with respect to the shell mold strength. Preferably theshell should be cast without additional external support because of thecost of supporting techniques known in the prior art. On the other handall known shells are subject to failure for one of two reasons whenlarge castings are considered. Shells generally fall into two classes,those using binders and refractories which break down at relatively lowtemperatures, causing distortion of large castings; and those using ahigher refractory with surface sintering of the particles functioning asa binder. This latter type of shell is less likely to distort due to itsgreatly increased strength but it is likely to cause hot tearing in thecasting. Neither type of shell therefore completely solves the problemof casting the heavier class of castings.

The invention enables the use of either type of shell in effecting aconsistent cast dimension without the above enumerated problems. In thecase of the low refractory shell, side wall bulging is prevented due tothe cooling support. The sintered shell may be cast with less wallthickness, thus avoiding the hot tearing problem due to the strength ofthe shell.

Thus while a preferred embodiment of the invention has been shown anddescribed, various additional modifications thereof will be obvious tothose skilled in the art and it will be understood that the invention isnot intended to be limited to the preferred embodiment or to detailsthereof and departures may be made therefrom within the spirit and scopeof the invention as defined in the claims.

I claim:

1. The method of supporting and cooling a refractory shell moldcomprising the steps of placing the shell on a bed containing amultiplicity of discrete particles of heatconductive material, pouringmolten metal into said shell, subjecting the bed to gas under pressurefrom below to cause the particles in said bed to be displaced from oneanother so that said shell mold is permitted to sink into said bed, andreducing said pressure so that the particles tend to fall back intosurrounding and supporting relationship about the mold to provide acontrolled cooling environment for the mold.

2. The method of supporting and cooling a refractory shell moldcomprising the steps of providing a bed comprising a multiplicity ofdiscrete particles of heat-conducting medium, introducing a supply ofcompressed air into said bed to cause the particles to be displaced fromeach other, lowering a shell mold partially into said displacedparticles, removing the air supply that said particles tall by gravityto rigidly support and position the shell mold, pouring molten materialinto the shell mold so supported, applying air to said bed to displacethe particles, permitting the filled shell mold to descend to apredetermined depth, and removing the air pressure so that said bedsupports said shell in a gas permeable heat sink medium for cooling saidfilled shell mold.

3. The method as claimed in claim 1 wherein said bed comprises aplurality of difierent chilling media having various specific gravitieswhereby they tend to be displaced vertically in layers throughout thebed under the influence of pressure applied to the bed and to remain insuch layers after the removal of pressure.

4. The method of supporting a thin walled gas permeable refractory shellmold filled with molten metal for cooling comprising the steps ofplacing the shell mold on a bed containing a multiplicity of particlesof heatconductive material, subjecting said bed to gas under pressure tocause said particles to be displaced so that said bed tends to act likea fluid permitting said shell mold to sink therein, and removing thepressure from said bed so that said particles tend to closely surroundsaid mold in supporting and cooling relationship.

5. Apparatus for supporting shell molds and con trolling the coolingrate thereof comprising a plurality of containers mounted on conveyingmeans for movement past a mold loading station, a pouring station and amold unloading station, each container being open to the atmosphere atthe upper side thereof and bounded on the lower side by a gas permeablemembrane, a bed formed of a multitude of discrete particles disposed ineach said container and supported on said membrane to provide a gaspermeable heat sink, and means to apply a gas under pressure throughsaid membrane to said bed for causing the particles therein to rise andseparate slightly so that a mold placed on said bed at said loadingstation will tend to sink therein, said mold being securely supported bysaid particles upon removal of said pressure from said membrane suchthat a mold filled with molten material at said pouring station and sunkin said bed may cool at a controlled rate.

6. The apparatus as claimed in claim 5 wherein the particles in said bedcomprise several different materials, each material having a difierentspecific gravity and each possessing different thermal transfercoefllcients such that the different particle materials tend to bedisplaced vertically in layers throughout the bed under the influence ofsaid gas pressure and to remain in such layers after the removal of saidpressure.

References Cited in the file of this patent UNITED STATES PATENTS2,660,770 Davis Dec. 1, 1953 2,718,041 Georgen Sept. 20, 1955 2,778,077Andrews Jan. 22, 1957 2,800,692 Cooke July 30, 1957 2,815,550 Volyi Dec.10, 1957

